Heldon Foyle had been prepared to take any risk rather than allow the Princess Petrovska to escape him again. There was nothing against her but suspicion. It was for him to find evidence that might link her with the crime. It is in such things that the detective of actuality differs from the detective of fiction. The detective of fiction acts on moral certainties which would get the detective of real life into bad trouble. To arrest the Princess was out of the question; even to detain her might make matters awkward. Yet the superintendent had made up his mind to afford Wills the butler a sight of her at all costs. If Wills identified her it would be at least another link in the chain of evidence that was being forged. He carried the butler in a taxicab with him to the nearest corner to the Duke of Burghley's house. A well-groomed man sauntered up to them and shook hands warmly with Foyle. "She has not come out yet," he said. "Good," exclaimed Foyle. "Come on, Wills. You have a good look at this woman when she does come out, and stoop down and tie your shoe-lace if she's anything like the woman who visited Robert Grell on the night of the murder. Be careful now. Don't make any mistakes. If you identify her you'll probably have to swear to her in court." "But I never saw her face," complained Wills helplessly. "I told you I was not certain I'd know her again." He was palpably nervous and unwilling to play the prominent part that had been assigned to him. Foyle laughed reassuringly. "Never mind. You have a look at her, old chap. You never know in these cases. You may remember her when you see her. Every one walks differently, and you may spot her by that. It won't do any harm if you don't succeed." He led Wills to a spot a few paces away from the house, but out of view of any one looking from the windows, and gave him instructions to remain where he was. He himself returned to the corner where Taylor, the detective-inspector who had greeted them when they drove up, was waiting. The other end of that side of the square was guarded by one of Taylor's assistants. Lola was trapped--if Foyle wished her to be trapped. He beckoned to a uniformed constable who was pacing the other side of the road. The man nodded--detectives whatever their rank are never saluted--and took up his position a few paces away. They had not long to wait. A taxicab whizzed up to the house, evidently summoned by telephone. Wills was staring as though fascinated at the slim, erect figure of the woman outlined on the steps of the house. He half stooped, then straightened himself up again. The superintendent muttered an oath under his breath and nodded to the loitering policeman. The constable immediately sprang into the roadway with arm outstretched, and the cab, which was just gathering way, was pulled up with a jerk. The blue uniform is more useful in some cases than the inconspicuous mufti of the C.I.D.